The present invention relates generally to a test adapter and, more particularly, to a test adapter for use with a SOIC (small outline integrated circuit) carrier or package.
A SOIC is a rectangular integrated circuit with inputs/output leads positioned on two of its four sides. The lead count ranges from eight pins to twenty-eight pins. There is presently available on the market today a test adapter for SOIC carriers which is somewhat similar to the test adapter for dual in-line (DIP) packages disclosed in U.S. Pat. No. Re. 28,064, except that it is smaller to accommodate the smaller SOIC carrier. The SOIC test adapter comprises two pivotally mounted contact housings. The adapter is operated by squeezing the two contact housings between the thumb and forefinger, similar to a clothespin. The contact housings rotate about a pivot pin located near the center of the device, thereby opening up the lower part of the adapter. The adapter is then positioned over the SOIC carrier and released. To remove the adapter one squeezes the top of the contact housings together and lifts the adapter up off the carrier.
The prior art SOIC adapter requires a heavy compression spring to provide the clamping force between the adapter and the carrier. In spite of the use of such compression spring, the adapter does not always drip the SOIC carrier securely. Furthermore, the adapter has a relatively high profile, which causes it to be somewhat unstable, with the result that occasionally the adapter will snap off the carrier with only minor movement or pressure. Further, often such a prior art SOIC adapter takes up more space when used to test circuit components on a board than is available.
Another prior art test adapter relevant to the present invention, which is designed for use with DIP's, comprises two contact frames which are pivotally mounted relative to each other by a longitudinally extending pin. Springs are mounted in the interior of the upper regions of the contact frames below the pivot pin, which tend to cause the lower ends of the frames to be biased apart. A rectangular shaped cam device surrounds the contact frames. When the cam device is pushed downwardly, the inside surfaces of the long sides of the device bear against the outside surfaces of the contact frames, camming them inwardly to cause the lower ends of the contacts in the frames to engage the leads on a chip carrier over which the clip is mounted.
Test adapters are also available and disclosed in the patent art which are used with PLCC's (plastic leaded chip carriers). PLCC's are flat four-sided integrated circuit packages with input/output leads on all four sides. The lead count ranges from 20 pins to 124 pins. U.S. Pat. Nos. 4,541,676; 4,671,590 and 4,671,592 disclose such test adapters. In each adapter, a spring is utilized either in conjunction with the contact housings, or latch arms which retain the adapter on the carrier. Copending application of W. D. Hansen entitled "Test Adapter for Integrated Circuit Carrier". Ser. No. 944,774, filed Dec. 22, 1986, now U.S. Pat. No. 4,735,580, assigned to the assignee of the present application, dislcoses a PLCC test adapter which is operated by placing the adapter over the PLCC, and then pushing down a locking wedge which rotates the outer contact housings about the center section of the adapter. When actuated, the contact housings grip the carrier leads on all four sides. This adapter does not utilize springs as do the other other PLCC adapters discussed above. However, because the Hansen adapter is constructed for use with PLCC's having leads on their four sides, it it not suitable for use with a SOIC.
It is the object of the present invention to provide a test adapter particularly suited for use with a SOIC carrier, which has a relatively low profile and therefore is stable, is simple in construction and avoids the use of springs.